(a) Field of the Invention
This invention relates to dental adhesive compositions which have excellent bonding properties and are useful in bonding dental restoration materials (such as metals, organic polymers and ceramics) to living tooth tissues.
(b) Description of the Prior Art
In the field of dental materials, a variety of materials have conventionally been used for the purpose of restoring carious teeth, missing teeth and the like. Such materials include metals such as gold, silver, platinum, alloys and amalgam; organic polymeric matrials such as polymethyl methacrylate, polycarbonate, cured products of multifunctional vinyl monomers, and so-called composite resins comprising such polymers having fillers incorporated therein; and ceramic materials such as porcelain.
However, these materials are inherently hard to bond to living dental tissues.
Accordingly, in order to enhance the bonding properties between the above-described restorative materials and the constituents of the tooth tissues, including inorganic components such as calcium phosphate (e.g., hydroxyapatite) and organic components such as collagen, there have been proposed a number of dental adhesive compositions in which a compound having a phosphate, hydroxyl or acid anhydride group, such as 2-methacryloyloxyethylphenylphosphoric acid, 2-hydroxy-3-.beta.-naphthoxypropyl methacrylate or 4-methacryloyloxyethyltrimellitic acid anhydride, is used as the adhesive component.
However, adhesives having the above-described functional group (i.e., a phosphate, hydroxyl or acid anhydride group) are generally poor in radical polymerizability at room temperature. Moreover, since dentin has a significantly higher protein content than enamel and contains a large number of dentinal tubules filled with a body fluid, adhesives having a polar group as described above are not suitable for use in bonding to dentin. In fact, it has often been the case that they exhibit no bonding power to dentin.
For these reasons, the above-described adhesives require pretreatment of the tooth apatite with an etching agent such as phosphoric acid.
However, even if such pretreatment is made, the above-described adhesives still fail to exhibit satisfactorily high bond strength. Moreover, the pretreatment cannot be continued for a longer period of time because it may be harmful to the tooth. Thus, if such an adhesive is used to bond a restorative material to a tooth, a gap will be produced between the restorative material and the dentin in a long period of time and, in the worst case, the restorative material may fall off.